EP4321271B1 - Method of manufacturing a motor vehicle component by hot forming with integrated trimming - Google Patents

Description

The present invention relates to a method for producing a motor vehicle component by hot forming and hot cutting according to the features in claim 1

Hot forming processes for sheet metal blanks are well known from the state of the art. Hot forming and press hardening are particularly well known. For this, a sheet metal blank made of a hardenable steel alloy is heated to a temperature above the Ac1 or Ac3 point. The blank heated in this way is then placed in a forming tool and formed while warm. The forming tool is then closed in a direct hot forming process and cooled quickly so that the formed blank is hardened. Tensile strengths of more than 1400 MPa are easily possible using the state of the art. The special feature is that the hardened material structure can then only be mechanically reworked with greater effort. This greater effort includes, for example, edge trimming. Edge trimming is usually carried out after the forming process in order to achieve a particularly high level of precision in the component. The component precision is therefore particularly accurate with regard to the outer contour. The problem, however, is that the already hardened board can only be hardened with great construction effort and high abrasive wear of the tool. Laser cutting also leads to high costs in the Manufacturing or production of the component. Cold cutting of hardened components is not recommended due to the risk of (micro)cracks.

The problem of edge trimming may be exacerbated as a further special feature when the blanks have different wall thicknesses, particularly in the case of Tailor Welded Blanks (TWB), blanks that are welded together from different wall thicknesses or steel alloys. Weld seam protrusions, weld seam collapse (inward notch) beyond the blank edge contour or even a blank offset between the two connected blanks are problematic and usually require re-trimming after the TWB has been welded together.

From the EN 10 2018 215 545 B4 or the EN 10 2020 201407 A1 A combined hot forming and cutting tool is known. At the end of the forming process or after the forming process has been completed, a final conformal edge trim is carried out. The object of the present invention is to show a possibility of producing a component by hot forming in a particularly cost-efficient manner and at the same time with increased precision.

The above-mentioned object is achieved according to the invention with a method for producing a motor vehicle component by hot forming and hot cutting with the features in claim 1. Advantageous further developments are described in the dependent claims.

The method according to the invention is used to manufacture a motor vehicle component. The motor vehicle components can be, for example, a motor vehicle B-pillar, a motor vehicle pillar in general, a tunnel, a bumper or bumper support or similar. In particular, flangeless reinforcement components that are at least partially U-shaped in cross section can also be manufactured in this way, as they are often used as insert components or patches to reinforce the above-mentioned components inside or outside and to form a local double sheet layer. These are manufactured by hot forming and hot cutting, and optional press hardening in a combined tool. Everything is carried out in one press stroke.

According to the invention, the method is characterized in that the inserted blank is already cut before the start of forming or in the first period of forming and the trimming is completed during this period.

The edge trimming is completed at least 20 mm, preferably more than 30 mm, in particular more than 50 mm, very particularly preferably more than 80 mm and in particular more than 100 mm before reaching the bottom dead center of the hot forming tool.

There is only a vertical cutting movement on the edge trim. The cutting tool itself is driven exclusively by the press stroke itself. There are no other active drives exclusively for the cutting tool. There are also no wedge cross slides. Trimming in the horizontal direction does not take place. These measures according to the invention make it possible to manufacture C-shaped or hat-shaped components with high tolerance requirements in cross-section. Furthermore, components can also be manufactured from tailor welded blanks or plates with different areas with different wall thicknesses. In particular, no subsequent trimming as tolerance trimming is required here. There are also no insertion tolerances compared to separate pre-insertion in the hot forming tool or pure blank trimming beforehand.

Furthermore, it is possible to produce U-shaped or C-shaped formed components in cross-section, i.e. flangeless components which, due to the vertical orientation of the U-shaped or C-shaped legs, could not be trimmed in a press after completion of the forming process or could only be trimmed with great effort.

In particular, the method provides that the blank is placed in the hot forming tool at a temperature greater than 500° C, in particular greater than 550° C. Preferably, the blank can also be placed in the hot forming tool at a temperature greater than AC1 or greater than AC3. Depending on the steel alloy used, the Ac1 temperature is more than 700° C, the Ac3 temperature more than 900° C.

To ensure that the blank is fixed in position, a punch is arranged on the upper tool that leads the upper tool. The blank inserted into the hot forming tool is placed on a lower mold jaw. The punch is then lowered onto the blank and clamps the blank in position between the punch and the lower mold jaw. The hot cutting process is then carried out. This can be done before the actual forming process begins.

The hot cutting process is carried out in particular as at least partial, in particular completely circumferential edge trimming of the blank. For this purpose, an externally rotating cutting tool is provided on the actual hot forming tool. The edge trimming can also be carried out completely in such a way that a partial circumferential blank is cut first, in particular before the blank is heated. During the hot cutting in the local forming tool, the remaining edge trimming then takes place, so that in total a completely circumferential edge trimming is carried out. In particular, no Subsequent edge trimming is no longer necessary. In particular, lasering or hard cutting is no longer required.

The cutting tool can be arranged completely relative to the upper tool and the lower tool. However, the cutting tool can also be integrated into the upper tool and/or the lower tool, thus into an upper mold jaw and/or a lower mold jaw.

As an alternative to complete edge trimming before the start of forming, it is also possible for the edge trimming to be carried out at an initial time or in the first phase of the forming process. In particular, the edge trimming is carried out when the blank itself is still completely in a flat, horizontal state or with a low degree of forming. This is particularly the case during a period of less than 50%, in particular less than 30%, in particular less than 20%, of the forming progress.

Alternatively or additionally, this period can also be related to the total press stroke of the upper tool and lower tool relative to each other. In particular, the cutting process has started and is completed at least 20%, preferably more than 30%, in particular more than 50% of the press stroke before the bottom dead center is reached, i.e. the forming tool is completely closed. In the case of 50%, this means that the edge trimming is completed when the upper tool is lowered onto the lower tool, based on the total press stroke, that this has progressed a maximum of 50% and in particular before the press stroke reaches the bottom dead center of the forming tool.

Following edge trimming, the hot forming process is then carried out or completed and optional press hardening takes place, especially if a hardenable steel alloy is used.

The edge trimming cuts through the board completely in its wall thickness.

The edge trimming is carried out in particular at a temperature of 550° to 700° C. It has been found according to the invention that at this temperature, depending on the steel alloy used, an optimum is achieved between the cutting ability of the steel and abrasive wear on the cutting tools, in particular also in the material structure that develops at the cutting edge.

Once the edge trimming has been carried out, the trimmed blank to be formed is drawn into the interior of the resulting mold cavity. Any bent legs of the resulting motor vehicle component or formed component can then run vertically oriented, so that vertically oriented trimming may not be possible.

This is solved according to the invention by a preliminary edge trimming in the horizontal state of the board.

In the context of this protective right, the terms hot forming tool and hot cutting tool are also used for the forming and cutting tool.

Figur 1a bis 1c

ein erfindungsgemäßes Umform- und Schneidewerkzeug

Figur 2a bis 2c

Abwandlungen zu Figuren 1a bis 1c

Figur 3a bis 3d

die Herstellung eines Kraftfahrzeugbauteils 13 als hutförmiges Bauteil

Figur 4a + 4b

zwei vorgefertigte Platinenbereiche

Further advantages, features, properties and aspects of the present invention are the subject of the following description. These serve to facilitate understanding of the invention. Preferred embodiments are shown in schematic figures. They show:

Figure 1a to 1c

an inventive forming and cutting tool

Figure 2a to 2c

Variations to Figures 1a to 1c

Figure 3a to 3d

the manufacture of a motor vehicle component 13 as a hat-shaped component

Figure 4a + 4b

two prefabricated circuit board areas

In the figures, the same reference symbols are used for identical and similar components, even if a repeated list is omitted for reasons of simplification.

Figures 1a , 1b and 1c show a forming and cutting tool 1 according to the invention. The forming and cutting tool 1 has an upper tool 2 and a lower tool 3. In the upper tool 2 itself, a leading punch 4 is arranged, which clamps a blank 6 placed on a lower forming jaw 5 of the lower tool 3. The leading punch 4 has been lowered beforehand. The blank 6 is thus fixed in position and can no longer be moved, in particular in the horizontal direction H. On an upper forming jaw 7, which is part of the upper tool 2, and a lower sheet holder 8, which is part of the lower tool 3, corresponding opposite cutting edges 9 are now arranged.

By further lowering, shown in Figure 1b , the upper mold jaw 5 is subjected to an edge trim 10. The edge trim 10 corresponds to the later outer peripheral component edge 11, shown in Figure 1c .

At the time of Figure 1b the forming process itself has not yet begun. However, the edge trimming 10 has been completed. By further lowering the upper forming jaw 7, the sheet holder 8 is lowered relative to the lower forming jaw 5. According to Figure 1c the forming process then takes place in a resulting mold cavity 12. The forming process is shown as completed and results in a cross-section of a flangeless motor vehicle component 13 that is U-shaped at least in length sections. The motor vehicle component 13 is made from the blank 6 to be formed. The blank 6 has been drawn into an interior of the forming tool or into an interior of the mold cavity 12.

In Figure 1a Cooling channels 19 can be seen, which can be provided for cooling all tool parts in contact with the formed blank for carrying out the press hardening. The cooling channels 19 are in the other Figures 1b - 3c not shown, but always provided on the tool.

Figures 2a to 2c show a variation of Figures 1a to c. Here too, the edge trimming 10 is carried out completely before the start of the forming process. In contrast to Figure 1c However, no motor vehicle component 13 with a U-shaped cross-section is produced here, but according to Figure 2c a motor vehicle component 13 with a hat-shaped cross section. Flanges 14 projecting outwards protrude in the horizontal direction H. For this purpose, the lower sheet holder 8 in particular is made wider and also serves to form a mold cavity 12 when the upper tool 2 is completely lowered to the bottom dead center.

Figures 3a to 3d show the manufacture of a motor vehicle component 13 as a hat-shaped component analogous to Figure 2c . However, the edge trimming 10 is only carried out at a later point in time, i.e. at a point in time when at least 20 mm of travel in the press stroke direction 15 must still be covered before the bottom dead center of the forming tool is reached. Here too, according to Figure 3b the inserted blank 6 is fixed in position on the lower mold jaw by the leading punch 4. However, the forming process has Figure 3b already started. The cutting tools or the opposing cutting edges 9 then carry out the cutting operation according to Figure 3c Here, for example, the forming process has progressed to approximately 20%, or the forming tool has been lowered in the press stroke direction 15 by approximately 20% of the distance to be covered by the press stroke. The edge trimming 10 is already completely finished at this point, so that according to Figure 3d , upon further lowering of the upper mold jaw and forming in conjunction with the lower sheet metal holder 8, the motor vehicle component 13 is then produced in the mold cavity 12 with flanges 14 projecting outwards in the horizontal direction H.

Figure 4 shows two prefabricated circuit board cuts. In the case of Figure 4a a Tailor Welded Blank. There are two blank areas 6a and 6b with different wall thickness. The blank areas 6a and 6b have an offset 16 to each other. Due to the circumferential edge trim 10, this offset 16 can be neglected, since a not in Figure 4a a closer set peripheral edge is re-cut again in the course of the method according to the invention and no final edge trimming 10 or the like would have to be carried out.

In case of Figure 4b A blank 6 is also shown as a tailor welded blank. A weld seam 17 connecting the two blank areas 6a and 6b has a lateral protruding weld seam projection 18. In the case of the circumferential edge trim 10, this weld seam projection 18 is also cut off.

Reference number:

1 -

Forming and cutting tools

2 -

Upper tool

3 -

Lower tool

4 -

Rubber stamp

5 -

lower mold jaw

6 -

circuit board

7 -

upper mold back

8th -

Sheet metal holder

9 -

Cutting edge

10 -

Edge trimming

11 -

Component edge

12 -

Mold cavity

13 -

Automotive component

14 -

flange

15 -

Press stroke direction

16 -

Offset

17 -

Weld

18 -

Weld protrusion

19

Cooling channel

6a -

Board area

6b -

Board area

H -

Horizontal direction

Claims (10)

1. Method of manufacturing a motor vehicle component (13) by hot forming and hot cutting and press hardening:

   - providing a blank (6) made from a hardenable steel alloy sheet,

   - complete heating to a temperature greater than Ac1, in particular greater than Ac3,

   - laying into a combined forming and cutting tool (1), wherein the forming and cutting tool (1) comprises a bottom tool (3) and a top tool (2); wherein the bottom dead point is achieved when the top tool (2) is completely lowered or when the forming tool is completely closed,

   - fixing the laid-in blank (6) in the forming and cutting tool (1) using a stamp (4) arranged in the interior of the tool,

   - carrying out an at least partially peripheral edge cut (10) prior to starting the forming or carrying out the edge cut (10) at least 20 mm prior to reaching the bottom dead point, wherein the cutting tool is driven exclusively by a pressing stroke of the forming and cutting tool (1),

   - hot forming in the pressing stroke with the edge cut (10) and press hardening.
2. Method according to claim 1, characterised in that the edge cut (10) is carried out across the entire periphery.
3. Method according to claim 1 or 2, characterised in that the edge cut (10) separates the blank (6) completely in its wall thickness.
4. Method according to any of the preceding claims, characterised in that the motor vehicle component (13) is U-shaped or hat-shaped in cross-section.
5. Method according to any of the preceding claims, characterised in that the edge cut (10) is carried out at 550° to 750°C.
6. Method according to any of the preceding claims, characterised in that the blank (6) to be formed is drawn into the interior of the forming tool by the further forming procedure after the cut has been carried out.
7. Method according to any of the preceding claims, characterised in that a Tailor Welded Blank is formed, wherein the blank (6) has at least two regions with wall thicknesses and/or steel alloys different from one another.
8. Method according to any of the preceding claims, characterised in that the edge cut (10) is carried out 30 mm and most preferably more than 100 mm prior to reaching the bottom dead point.
9. Method according to any of the preceding claims, characterised in that the stamp (4) presses the blank (6) for fixing onto a bottom forming jaw (5) of the tool.
10. Method according to any of the preceding claims, characterised in that the stamp, the forming jaw and all further tool parts, the tool parts which are in contact with the blank (6) formed to form the motor vehicle component (13) are actively cooled for press hardening.

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